Effects on Three-Dimensional Geosynchronous Circular SAR Imaging by Orbit Errors
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RESEARCH ARTICLE
Effects on Three-Dimensional Geosynchronous Circular SAR Imaging by Orbit Errors Leilei Kou & Xiaoqing Wang & Maosheng Xiang
Received: 4 June 2012 / Accepted: 27 May 2013 # Indian Society of Remote Sensing 2013
Abstract Circular SAR imaging on the geosynchronous orbit is an innovative SAR imaging mode, which can perform high resolution three-dimensional (3D) imaging with continuous observations for a large area. However, for geosynchronous satellites the orbit is severely disturbed by perturbing effects, and the orbit error will be an important factor influencing the SAR imaging on the geosynchronous orbit. In this paper, the effects of the orbit error on performances of 3D geosynchronous circular SAR (GEOCSAR) imaging are analyzed. The error model is firstly made, and then the orbit error propagating into the distance from the radar to the target (range) is derived. Furthermore, the effects of different components of the range error on the quality of focused SAR signals are deduced, based on the 3D GEOCSAR signal model with time-domain correlation algorithm. The analyses and simulations will quantify and verify the required accuracies of GEOCSAR orbit estimation for ensuring the 3D imaging quality. Keywords Geosynchronous circular SAR (GEOCSAR) . Three-dimensional (3D) imaging . Orbit error . Range error L. Kou (*) Nanjing University of Information Science and Technology, No.219, Ningliu Road, Nanjing 210044, Peoples Republic of China e-mail: [email protected] X. Wang : M. Xiang Institute of Electronics, Chinese Academy of Sciences, Beijing 100190, Peoples Republic of China
Introduction A geosynchronous SAR (GEOSAR) concept has previously been presented by Tomiyasu (1983). The synthetic aperture is obtained with an apparent motion of the geosynchronous satellite induced by non-zero inclination and eccentricity of the orbit (Soop 1994; Cazzani et al. 2000; Prati et al. 1998). With about 36000 km altitude, the GEOSAR can offer coverage as wide as over 1000 km (Chi and Su 1995). Since the GEOSAR could not only offer continuous surveillance for broad areas, but also can perform 3D deformation measurement with interferometric processing, it has been a research hotspot in recent years (Madsen et al. 2001; NASA 2003; Bruno and Hobbs 2006; Kou et al. 2010; Hu et al. 2011). In the previous researches, the inclined geosynchronous orbit is chosen to offer the linear track, so the SAR can work as the traditional sidelook strip mapping SAR (Colesanti and Perissin 2006). With appropriate geosynchronous orbital parameters, the geosynchronous orbit can offer much more flexible satellite track than low earth orbit, such as circle, ellipse, 8-like and some other complex tracks. Thus, the circular SAR (CSAR) imaging mode can be realized on the geosynchronous orbit if the satellite track is designed to be near circular (Kou et al. 2012). The circular satellite track can provide true 3D image with improved ground resolution (Wang 2007; Axelsson 2004), and a geosynchronous satellite will provide a steady and approp
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